Request for some insights into a pointer grabbing + pointer emulation issue.

Daniel d'Andrada daniel.dandrada at
Tue Nov 20 04:04:24 PST 2012

On 19/11/12 03:56, Peter Hutterer wrote:
> On Wed, Nov 14, 2012 at 03:37:05PM -0200, Daniel d'Andrada wrote:
>> I've been investigating an issue where xserver simply stops sending
>> ButtonPress and ButtonRelease events, out of touch events, to a window.
>> I've spent already quite a few days studying the issue, looking at the
>> pointer grabbing + pointer emulation logic, and although progress has
>> been made, I fear reaching insanity before finally cracking it. :)
>> I've a good amount of information in a log, so my hope is that some
>> expert in (or author of) the touch input code (e.g. Peter Hutterer)
>> might be able to shed some light on the issue without much effort.
>> Here's is the situation:
>> The setup is a touchscreen laptop running Ubuntu.
>> I just repeatedly tap on the top-most icon (the one which has the Ubuntu
>> logo) of Ubuntu's launcher. Those taps alternately open and close the
>> dash (a fullscreen window that shows icons for applications, media and
>> other files). At some point those taps stop having any effect. I.e., the
>> launcher no longer gets ButtonPress and ButtonRelease events out of them.
>> And here's is the corresponding log (from bug 56578):
>> From touches 2 to 26, launcher is the first window in the list of
>> listeners. From touch 27 onwards, the root window is the first one.
>> Problem is, from touch 27 onwards, xserver fails to pass the touch
>> ownership down to the launcher window because there's always an older
>> pointer-emulated touch (touch 26) lying around which it apparently can't
>> get rid of (i.e. properly process).
> just fyi, I am keeping an eye on this bug, I've just been busy with other
> stuff for the last couple of days. I'm pretty sure this is also influenced
> by this bug here:
> which causes some issues with pointer emulation on the root window, so if
> you can test with these 3 patches + the one I just sent out that'd be quite
> appreciated.

Hi Peter,

I applied all the 4 patches mentioned and they have actually made
situation worse. :(
Right now I'm busy with other tasks so can't provide any further info on it.

- Daniel

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